1. Field of the Invention
The present invention relates to the use of integrally formed polymeric grid structures possessing high structural integrity, elasticity and high tensile strength such that they are capable of being significantly, predictably and repeatedly deformed under stress without breaking, supporting significant load as they approach the limit of their elasticity and returning to substantially original shape when the deforming stress is removed. The present invention is suitable for use in load support applications requiring controlled elasticity and high durability such as in seat fabrication for aircraft, automobiles and other means of personal transportation; or in bedding and furniture fabrication or in similar load support systems used in commercial, industrial and recreational applications.
The present invention is economically superior to known competitive materials possessing comparable performance capabilities, which typically embody steel spring mechanisms and multiple component fabrications to achieve desired mechanical properties.
The present invention is mechanically and economically superior to known competitive materials embodying polymeric materials possessing elastic properties, which typically fail prematurely at their junction points if fabricated in a mesh or net configuration, or which typically embody substantially more material and substantially more capital and labor intensive processing than the present invention if fabricated in a woven or knitted or sheet configuration.
2. Description of the Prior Art
Load support systems used in seating, bedding and furniture fabrications and similar applications have evolved over all of recorded history. Initial structures were rigid, fabricated of wood, stone, metal and the like, and were typically covered with some sort of cushioning material to improve comfort in seating or sleeping or to achieve similar effects in other applications. Limited amounts of flexibility were later incorporated in load support systems through use of woven strips and filaments of natural materials such as cotton, jute and the like which were typically fabricated to form sheet like suspension systems mechanically fastened at their perimeter to rigid frames. Various spring steel mechanisms were later incorporated to increase the elasticity of the load support system, to improve its ability to return to substantially original shape when loads were removed, and do so after numerous load cycles, and to improve useful service lives. The use of rigid wire platforms connected to rigid wood or steel frames via extensible steel spring mechanisms and then covered with various cushioning materials remains today the preferred embodiment for achieving comfort and durability in use in most seating applications. It is, however, a relatively expensive embodiment involving numerous independent fabrication processes, considerable use of capital assets and labor resources in fabrication and in material handling and considerable material content. The use of steel material is also not optimal from the standpoint of weight, while the elastomeric suspension system of this patent specification has the advantage of providing improved performance together with structural light weight.
As numerous polymeric materials have been developed and improved, considerable attention has been devoted to using such materials to displace the traditional materials and traditional fabrication methods referenced above--primarily to reduce cost, but also to achieve performance, aesthetic and other benefits. Several such advances have been made in load support systems particularly in using polymeric materials to form rigid frames and to create cushioning materials suitable for use in seating, bedding and similar applications.
Analogous advances have also been sought in substitution of polymeric materials for the rigid wire platforms and spring steel connectors which are referenced above. For instance, woven and knitted polymeric filaments, straps and tapes have been substituted for the rigid wire platforms used in seating applications, and in some instances such materials have also substituted for spring steel connectors. In use such polymeric materials are mechanically fastened to rigid frames or are connected to rigid frames with spring steel connectors. As materials possessing improved elastic and elastic recovery properties have been developed, such embodiments have achieved some market acceptance and have successfully displaced traditional materials and traditional fabrication practices in some applications. However, most such displacement has been in lower cost, lower quality applications in which performance and durability tradeoffs have been accepted by users.
Attempts have also been made to use integrally formed polymeric mesh or net materials with elastic properties in substitution for rigid wire platforms and spring steel connectors and their competitive equivalents. However, these have not been successful to date in that such materials characteristically fail at the junction points of the mesh or net structure when subjected to high levels of deforming stress, or repeated deforming stress--or require excessive amounts of expensive material in their junctions to dissipate stress levels.
U.S. Pat. No. 4,869,554 to Abu-Isa discloses a vehicle seat assembly comprising elastomeric filaments woven into a net configuration and prestretched across a rigid frame.
U.S. Pat. No. 4,469,739 to Gretzinger discloses oriented woven furniture support materials made in part from elastomeric monofilament and in part from yarn. These furniture support materials can be made by weaving the elastomer in a first direction and the yarn in a second direction perpendicular to the first direction. The two series of strands may be bonded or fused at the crossover points. Both the Gretzinger and Abu-Isa processes produce a support material which is not integrally formed and where the junctions are biplanar, being made by strands which cross over each other at intersections.
U.S. Pat. No. 4,469,738 to Himelreich, Jr. discloses a furniture support material in a net configuration including crossed strands of oriented thermoplastic elastomers, such as a copolyetherester, which are bonded to each other at points at which they cross. This support material can be made by extrusion through a pair of close fitting concentric tubular dies one or both of which rotate in an opposing direction to the other or by weaving of filaments. The Himelreich process produces a biplanar structure in which the nodes, or points at which the strands cross, have a thickness which may be as great as the thickness of both individual strands. Such structures have inherent thickness variation with substantial continuity of each strand at the crossover points, producing biplanar junctions with reduced capability to resist breakage at high and/or repeated load levels. Himelreich does not disclose making such materials in a uniplanar grid configuration.
U.S. Pat. No. 3,252,181 to Hureau discloses a method for extruding polymeric material through reciprocating dies in which the polymeric material is periodically prevented from leaving the die at points which correspond to desired voids or openings and then allowed to leave the die at such points thereby creating an apertured material in a grid configuration which may be substantially uniplanar in cross section. Embodiments and methods disclosed by Hureau may be used for producing the integrally formed grid of the present invention.
U.S. Pat. No. 5,114,998 to Golder et al disclosed talc filled thermoplastic polyester compositions which have been modified by the addition of a butadiene-based impact modifier stabilized against degradation by the addition of a diphenylamine compound. The polyesters may be copolyetheresters which may be used to produce the present invention.
The materials of the present invention are manufactured from a continuous process which is inherently different from and economically superior to the weaving process disclosed in U.S. Pat. No. 4,469,739 which requires many independent manufacturing steps to convert raw material to final products. The materials of the present invention also differ from the furniture support material which is disclosed in U.S. Pat. No. 4,469,738. The materials of the present invention are formed from starting materials which are uniplanar or substantially uniplanar structures, whereas U.S. Pat. No. 4,469,738 discloses use of substantially biplanar structures made in accordance with U.S. Pat. No. 2,919,467. Integrally formed polymeric grid structures which are substantially uniplanar may be produced by methods disclosed in U.S. Pat. No. 3,252,181. When such integrally formed polymeric grid structures are extruded in a substantially uniplanar configuration and then mechanically stretched, the polymeric molecules comprising the materials experience uniform in-plane deforming forces which cause them to align themselves around the apertures in continuous repeating symmetrical three dimensional patterns centered on a median plane. However, if such integrally formed polymeric grid structures are extruded in a substantially biplanar configuration and then mechanically stretched, the polymeric molecules Comprising the materials experience widely varying deforming forces across their cross section, with such force applied as offset moments relative to the median plane of the material, the result of which is diminished suitability for use in load support applications as are intended for the present invention.